This invention relates to innerducts which facilitate the installation of communication and power transmission cables in existing conduits and, more particularly, to a prelubricated innerduct which provides a low friction and hazardless environment for the installation and placement of fiber optic cables.
Fiber optic cables are currently being provided as a substitute for a great deal of the copper cable heretofore utilized in the telecommunication industry. Fiber optic cables or "light guide" cables are preferred in that they are capable of transmitting a substantially greater amount of information while occupying a substantially smaller amount of space than conventional copper cable. The fiber optic cables are typically encased in a polyethylene sheath which acts as a protective coating for the fiber optic elements, which are formed from glass.
The cables are installed in innerducts which have been placed in existing, typically subterraneal, conduits from which the copper cables have been removed or in innerducts buried directly in the ground. The innerducts are used to provide for substantially low friction placement of and a hazardless environment for the fiber optic cable(s).
Nevertheless, it has been discovered that it is difficult to install innerducts into existing conduits because of the friction between the exterior wall of the innerduct and that the interior wall of the existing conduit. In addition, once the inner duct has been installed, there is friction between the inner wall of the innerduct and the fiber optic cables as they are inserted into and along the innerduct. To overcome these frictional problems, various water-soluable polymeric lubricants have been used. These lubricants are generally of the glycol type. However, because the existing conduits within which the innerducts are placed are typically 3-4 inch PVC pipe, 3-4 inch square terra cotta pipe or the like, the innerducts must have a rather small diameter. In addition, the innerduct itself can have a length of up to 10,000 feet or more. Therefore, the application of lubricant to the entire interior surface of the innerduct presents a substantial burden. Further, even if lubricant is applied to a substantial portion of the innerduct interior or to the cable itself, repeated relative sliding movement due to removing or replacing cables within the innerduct will reduce the amount of lubricant disposed therein Further, due to the time required to place long lengths of cable, liquid lubricants tend to dry, thereby losing their effectiveness before the placing operation is complete.
Yet another problem encountered with existing innerducts is that after the ducts are extruded, because of the great length required, the extruded tubing is immediately wrapped or rolled about a spool or the like for subsequent transport to a storage facility or installation location. Since the extruded material is so readily wrapped for transport, it has been found that the tubing may not be completely cooled prior to rolling. Accordingly, the tube's cross-sectional shape can be distorted into an ellipse that has a major dimension which prohibits the insertion thereof into an existing conduit and/or a minor dimension which prevents the placement of the desired diameter of fiber optic cable therein. Further, regions of potentially greater friction during installation are generated when the innerduct is distorted in this manner.